Comment by jiggawatts
21 hours ago
Apparently 14 K cooling is not used even up to 5N or 6N purity, commercial large-scale sources use various other tricks to remove the other gases. They do cool the input gas down to liquid nitrogen temperatures as one of the first steps.
My point is that there's "maximally efficient / profitable" versus "can be made available as an emergency alternative".
Cooling to 14 K isn't the cheapest option, but it has very low complexity. You can "simply" pressurise the source gas, cool it to room temperature through an ordinary heat exchanger, then allow it to expand. The only issue is that if you do this naively, the expansion nozzle will get clogged with ice.
Obviously, this wastes a lot of Helium, but we have lots of it. If what's needed is high purity Helium, then throwing away even 90% to get 10% that's 6N pure should be no problem for an industrial nation.
You can't just spin up such a facility in a few days or weeks though, surely? Even if the core of a process is relatively simple physically, you still need all the supporting infrastructure to make it happen.
Starting from an empty lot, no, it would take nearly a year.
However, any air (or gas) liquefaction / separation plant that is already making purified industrial gases from air or other sources could be adapted in a matter of weeks or at most a couple of months.